692 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



of Brontops robustus are not yet apparent. The 

 humerus {B. leidyi, Carnegie Mus. 93) is a relatively 

 very small bone (mid-length 380 mm.) with an 

 enormously expanded crest of the great tuberosity. 



FiQUBE 627. — Radius and ulna of 

 Brontotherium 



K, B. leidyi, Carnegie Mus. 93, outer side view 

 of radius and ulna; B, B. gigas, Am. Mus. 492. 

 One-eightli natural size. 



Its distal end is relatively narrower and higher than 

 in Brontops rohustus (type). The radius {B. leidyi, 

 Carnegie Mus. 93) is likewise very short (mid-length 



is markedly different from that of B. rohustus (type; ; 

 the styloid process is produced farther downward; 

 the external contour is more sharply concave; the 

 internal contour is straighter; the middle of the head 

 is less angulate. The ulna both in B. leidyi (Carnegie 

 Mus. 93, length 410 mm.) and in B. gigas (Am. Mus. 

 492, length 642 mm.) has the sigmoid notch much 

 less deeply concave in side view than in Brontops 

 rohustus; the shaft of the ulna appears to be more 

 slender, especially at the lower end. In B. gigas the 

 tuberosity of the olecranon (for the main mass of 

 the triceps) is widely expanded transversely. 



Manus of Brontotherium, U. S. National Museum 



The manus of Brontotherium is known from the 

 lunar of B. gigas (Am. Mus. 492) and from a mixed 

 lot of specimens in the National Museum (No. 4262; 

 see p. 690). 



This manus (fig. 631), which probably belongs with 

 the skull of B. gigas (Nat. Mus. 4262), is much smaller 



Figure 628. — Ulnae of Brontops robustus, Brontotherium leidyi, and Bronto- 

 therium gigas 



A, Brontops rohustus, Yale Mus. 12048 (type); B, Brontotherium leidyi, Carnegie Mus. 93; C, 

 Brontotlierium gigas. Am. Mus. 492. The proximal part of ttie ulna of Brontops is wider and tlie 

 olecranon is perhaps shorter than in Brontotlierium. One-eighth natural size. 



B C 



-Olecrana of Brontotherium and Mega- 

 cerops? 



End view. A, B. gigas, Am. Mus. 492; B, B. leidyi, Carnegie Mus. 

 93; C, Megacerops? sp.. Am. Mus. 351 (6351?). The olecranon of 

 the largest animal is greatly swollen. One-eighth natural size. 



than that referred to B. gigas (Am. Mus. 

 492), but it agrees in measurements and in 

 characters with another manus (Am. Mus. 

 1047) which is assigned provisionally to B. 

 Jiatcheri. Hence it seems probable that the 

 manus shown in Figure 631 represents a 

 female of either B. Jiatcheri or B. gigas. The 

 differences between the manus of Brontothe- 

 rium and that of Brontops rohustus are ex- 

 hibited in Figure 630. In general the manus 

 appears to be more compact and less spread- 

 ing, especially at the lower end, than that of 

 Brontops rohustus; the magnum is wider and 

 the lunar magnum articulation more extended; 

 there are also detailed differences in the 

 other carpal elements, but at present it is 

 not known whether any of these are constant 

 or how far they may be individual rather 

 than generic differences. 



305 mm.). Even in B. gigas (Am. Mus. 492, mid- 

 length 460 mm.) the radius is relatively shorter than 

 in Brontops rohustus (type) (mid-length 500). In both 

 species the whole contour of the radius in front view 



Pelves and hind limbs referred to B. gigas 

 Pelvis. — The pelvis of Brontotherium is known from 

 three specimens — a well-preserved pelvis of B. gigas 

 (Am. Mus. 492), associated with a skull and some 



